The present invention, in some embodiments thereof, relates to isolated polynucleotides expressing or modulating microRNAs or targets of same, transgenic plants comprising same and uses thereof in improving nitrogen use efficiency, abiotic stress tolerance, biomass, vigor or yield of a plant.
Consumption of soybean for food production is increasing worldwide because of its reported beneficial health effects. Soybean is also viewed as an attractive crop for the production of biodiesel. Importantly, it has the ability to fix atmospheric nitrogen, which in turn may cut the input of nitrogen fertilizer that often accounts for the single largest energy input in agriculture.
With a growing world population, increasing demand for food, fuel and fiber, and a changing climate, agriculture faces unprecedented challenges. In general, shortage in water supply is one of the most severe global agricultural problems affecting plant growth and crop yield. Excessive efforts are made to alleviate the harmful effects of desertification of the world's arable land. Farmers are seeking advanced, biotechnology-based solutions to enable them to obtain stable high yields and give them the potential to reduce irrigation costs or to grow crops in areas where potable water is a limiting factor. It should be noted that improved abiotic stress (ABST) tolerance will confer plants with improved vigor also under non-stress conditions, resulting in crops having improved biomass and/or yield.
ABST is a collective term for numerous extreme environmental parameters such as drought, high or low salinity, high or low temperature/light, and nutrient imbalances. The major agricultural crops (corn, rice, wheat, canola and soybean) account for over half of total human caloric intake, giving their overall yield and quality vast importance. ABST causes more than 50% yield loss of the above mentioned major crops. Among the various ABSTs, drought is the major factor that limits crop productivity worldwide. Short-term conditions of reduced environmental water content typically occur during the life cycle of most crop plants. Although most plants have evolved strategies to survive these conditions, when the severity and duration of drought become too great, major alterations to the plant metabolism take place. As a result, the plant development, growth and yield profoundly diminish. Furthermore, drought is associated with increased susceptibility to various diseases. ABST-induced dehydration or osmotic stress, in the form of reduced availability of water and disruption of turgor pressure, cause irreversible cellular damage. A water-limiting environment at various plant developmental stages may activate various physiological changes.
In soybean, drought, for instance, reduces yield by approximately 40%, with the most critical period for water deprivation being the flowering stage and the period following flowering. Water deficit, salinity and low/high temperatures are stresses that cause plant cellular dehydration, due to transpiration rate that exceeds water uptake. Water use efficiency (WUE), defined as the amount of biomass accumulated per unit of water used, plays an important role in determining a plant's ability to tolerate drought stress. The higher the WUE of a plant, the higher the crop productivity and total biomass yield under drought conditions. Thus, efforts are made worldwide to increase the WUE of the most important crops and reach the best yield performance under extreme water deficiency conditions.
Studies have shown that plant adaptations to drought and other adverse environmental conditions are complex genetic traits with polygenic nature. Conventional means for crop and horticultural improvements utilize selective breeding techniques to identify plants having desirable characteristics. However, selective breeding is tedious, time consuming and has an unpredictable outcome. Furthermore, limited germplasm resources for yield improvement and incompatibility in crosses between distantly related plant species represent significant problems encountered in conventional breeding. Advances in genetic engineering have allowed mankind to modify the germplasm of plants by expression of genes-of-interest in plants. Such a technology has the capacity to generate crops or plants with improved economic, agronomic or horticultural traits. However, generation of transgenic plants expressing full-length genes is typically hampered by the selection of optimal regulatory sequences and identification of those rare transformation events that exhibit sufficient levels of gene products expression.